It is well known that variable compression ratio (VCR) and variable expansion ratio (VER) for the internal combustion engine is a revolutionary technology with the most development potential in today's world. The technology plays a vital role to reduce carbon emissions, oil products, biofuels, and other fuel consumption. Despite of numerous inventions in the field, no commercialized engine has gone into the market, which implies the difficulty to capture the VCR and VER internal combustion engine technology.
In 1891, U.S. Pat. No. 460,642 to Kitson discloses a structure in a thermodynamic cycle that is pivotally mounted on the crankpin and through the rotation of the eccentric sleeve, changes the lengths of all the four strokes. In 1977, U.S. Pat. No. 4,044,629 to Clarke discloses a modification to the structure of Kitson with an added changing apparatus of the eccentric sleeve rotation angle so that the internal combustion engine is conveniently used in a variety of different conditions, part load and full load. The modification makes the efficiency of the internal combustion engine to exceed that of the Miller cycle, or Atkinson cycle. Unfortunately, the apparatus in the patent can only be carried out in a single-cylinder engine, which limits the application of the patent.
In 1999, U.S. Pat. No. 5,927,236 to Gonzalez and other similar patents have the same or similar effects of the one to Clark, however, because either the strength of the crankshaft is greatly reduced or the set of driving mechanism is too complex, it is difficult to achieve reliable operation with low cost. Thus, there is no practical use of the technology.
In 2002, U.S. Pat. No. 6,349,684 to De Gooijer achieves the same function as the patent to Clark and the apparatus may be used in two cylinders, four cylinders, and V-type internal combustion engines, which is the famous “GoEngine.” The efficiency of the VCR and VER engine is greatly enhanced. The apparatus in the patent is relatively simple, however, the planetary gear of the apparatus is placed in the main journal of the crankshaft, and in order to ensure the operation of the planetary gear, a huge space has been dug inside the main journal for placing the planetary gear, which greatly reduces the strength of the crankshaft. At the same time, the diameters of the crankpin and the planetary gear are designed to be smaller because of the limitation of the structure, thus, it is difficult to improve the strength of the crankshaft by increasing the size. In addition, the diameter of the ring gear is large while the meshing speed between the planetary gear and the ring gear is high, and the rigidity of the ring gear is insufficient, which impacts the NVH performance of internal combustion engine.